Soil Bearing Capacity and Load Calculator

ANA›Life Services Authority›National Calculator Authority›Soil Bearing Capacity and Load Calculator

.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }

Soil Bearing Capacity and Load Calculator

Calculate the ultimate and allowable bearing capacity of soil using Terzaghi's General Bearing Capacity Equation, and determine the maximum allowable structural load for a specified footing area.

### Soil Properties

Soil Cohesion, c (kPa)

Use 0 for purely granular (cohesionless) soils.

Internal Friction Angle, φ (degrees)

Typical range: 0° (soft clay) to 45° (dense gravel).

Unit Weight of Soil, γ (kN/m³)

Typical range: 14–22 kN/m³.

### Footing Geometry

Depth of Foundation, Df (m)

Depth from ground surface to footing base.

Footing Width, B (m)

Shorter dimension of the footing.

Footing Length, L (m)

Longer dimension. Set equal to B for square/circular footings.

Footing Type

Rectangular / Square Strip (Continuous) Circular

### Safety & Load

Factor of Safety, FOS

Typical value: 2.5–3.0 for foundations.

Applied Structural Load, Q (kN) (optional)

Leave blank to skip load check.

Calculate Bearing Capacity

Results will appear here.

function soiCalc() { // --- Read inputs --- const c = parseFloat(document.getElementById('soi-cohesion').value); const phi = parseFloat(document.getElementById('soi-friction').value); const gamma = parseFloat(document.getElementById('soi-unit-weight').value); const Df = parseFloat(document.getElementById('soi-depth').value); const B = parseFloat(document.getElementById('soi-width').value); const L = parseFloat(document.getElementById('soi-length').value); const FOS = parseFloat(document.getElementById('soi-fos').value); const Qraw = document.getElementById('soi-load').value.trim(); const Q = Qraw === '' ? null : parseFloat(Qraw); const ftype = document.getElementById('soi-footing-type').value;

// --- Validation --- const errors = []; if (isNaN(c) || c 45) errors.push("Friction angle (φ) must be between 0° and 45°."); if (isNaN(gamma) || gamma 0 kN/m³."); if (isNaN(Df) || Df f) must be > 0 m."); if (isNaN(B) || B 0 m."); if (isNaN(L) || L 0 m."); if (L 0) { resultDiv.innerHTML = 'Please fix the following:' + errors.map(e => '').join('') + ''; return; }

// --- Terzaghi Bearing Capacity Factors --- // Convert phi to radians const phiRad = phi * Math.PI / 180.0;

// Nq = e^(π·tan φ) · tan²(45 + φ/2) const Nq = Math.exp(Math.PI * Math.tan(phiRad)) * Math.pow(Math.tan((45 + phi / 2) * Math.PI / 180), 2);

// Nc = (Nq - 1) · cot φ [for φ > 0]; Nc = 5.14 for φ = 0 (Prandtl) const Nc = phi > 0 ? (Nq - 1) / Math.tan(phiRad) : 5.14;

// Nγ = 2·(Nq + 1)·tan φ (Meyerhof approximation) const Ngamma = 2.0 * (Nq + 1) * Math.tan(phiRad);

// --- Shape Factors (Meyerhof / De Beer) --- let sc, sq, sg; if (ftype === 'strip') { sc = 1.0; sq = 1.0; sg = 1.0; } else if (ftype === 'circular') { sc = 1.3; sq = 1.0; sg = 0.6; } else { // Rectangular / Square sc = 1.0 + 0.2 * (B / L); sq = 1.0 + (B / L) * Math.tan(phiRad); sg = Math.max(1.0 - 0.4 * (B / L), 0.6); }

// --- Ultimate Bearing Capacity (Terzaghi-Meyerhof) --- // qu = c·Nc·sc + γ·Df·Nq·sq + 0.5·γ·B·Nγ·sγ const qu = c * Nc * sc + gamma * Df * Nq * sq + 0.5 * gamma * B * Ngamma * sg;

// --- Net Ultimate Bearing Capacity --- // q_net_ult = qu - γ·Df (subtract overburden) const q_net_ult = qu - gamma * Df;

// --- Allowable Bearing Capacity --- // q_allow = q_net_ult / FOS (net allowable) const q_allow = q_net_ult / FOS;

// --- Gross Allowable (add back overburden) --- const q_allow_gross = q_allow + gamma * Df;

// --- Footing Area --- let A; if (ftype === 'circular') { A = Math.PI * Math.pow(B / 2, 2); // B treated as diameter } else { A = B * L; }

// --- Maximum Allowable Load --- const Q_max = q_allow * A; // kN (net basis)

// --- Load Check ---
let loadCheck = '';
if (Q !== null) {
const q_applied = Q / A; // kPa
const utilization = (q_applied / q_allow) * 100;
const safe = q_applied Applied Load Check
Applied Load (Q)${Q.toFixed(1)} kN
Footing Area (A)${A.toFixed(3)} m²
Applied Bearing Pressure${q_applied.toFixed(2)} kPa
Net Allowable Capacity${q_allow.toFixed(2)} kPa
Utilization Ratio${utilization.toFixed(1)}%
Status
${safe ? '✅ SAFE — Load within allowable capacity'
'❌ UNSAFE — Load exceeds allowable capacity'}`; }

// --- Output --- resultDiv.innerHTML = ` ### Results

ParameterValue Bearing Capacity Factors (Terzaghi-Meyerhof) Nc${Nc.toFixed(3)} Nq${Nq.toFixed(3)} Nγ${Ngamma.toFixed(3)} Shape Factors sc${sc.toFixed(3)} sq${sq.toFixed(3)} sγ${sg.toFixed(3)} Bearing Capacity Ultimate Bearing Capacity (qu)${qu.toFixed(2)} kPa Net Ultimate Bearing Capacity (qnet,ult)${q_net_ult.toFixed(2)} kPa Net Allowable Bearing Capacity (qallow)${q_allow.toFixed(2)} kPa Gross Allowable Bearing Capacity${q_allow_gross.toFixed(2)} kPa Maximum Allowable Load on Footing${Q_max.toFixed(1)} kN ${loadCheck} `; }

#### Formulas Used

Terzaghi-Meyerhof General Bearing Capacity Equation:

qu = c · Nc · sc + γ · Df · Nq · sq + 0.5 · γ · B · Nγ · sγ

Bearing Capacity Factors:

Shape Factors (De Beer / Meyerhof):

Net and Allowable Capacities:

#### Assumptions & References

More Calculators

Read Next

Study Time Planner Authority Network America › Life Services Authority › National Calculator Authority .calc-container { max-width: 640px;...

References

Related Authorities

Life Services Authority › Professional Services Authority › Trade Services Authority › United States Authority ›